1. Technical Field
This invention relates to a process for crushing a hafnium crystal bar, and more particularly to a process for crushing a hafnium crystal bar in order to produce a starting material for the production of a high-purity fine powder of hafnium having superior toughness and heat resistance.
2. Background Art
Recently, hafnium (Hf) has drawn attention in various fields because of its superior toughness and heat resistance. For instance, in the field of precision casting, unidirectionally solidified materials of super heat-resistant nickel-base alloys with Hf contained therein are being commercialized. In the field of powder metallurgy, also, not only Hf-containing heavy alloys and dispersion-strengthened alloys but HfC- or HfN-containing composite carbides are being commercialized.
In the former case, hafnium has been added in the form of crystal bars in the production of a master ingot as a starting material or a raw material. The Hf crystal bars in their uncrushed state have led to low yields or have caused segregation.
In the latter case, on the other hand, it has been the common practice to reduce a hafnium salt by hydrogen to form Hf or then form a carbide therefrom. In the process of production of the alloys or carbides, however, the decomposition or escape of unrequired elements or groups contained in the Hf salt has often resulted in formation of vacancies and a disordered crystal structure in the final product.
The above-mentioned problems are solved if there is a crushed product of Hf crystal bars of maximum purity as the starting or raw material. Because of the high hardness, high toughness and the close-packed hexagonal crystal structure of the Hf crystal bars, however, there has not been a conventional technique to crush the Hf crystal bars, and commercialization has therefore been carried out simply by crushing Hf sponge.
When the Hf sponge is crushed for use as a raw material for a variety of uses, the physical properties and workability of the final product are lowered, because of the high nitrogen and oxygen contents of the raw material and the susceptibility of hafnium to the effects of interstitial impurities such as nitrogen and oxygen.
In addition, in the process of producing the Hf sponge, chlorine and magnesium are left in the Hf sponge. Therefore, the Hf sponge has a high content of chlorine and magnesium, which leads to a deterioration of the physical properties of the final product.